Chemical vapor deposition system with a plasma chamber having separate process gas and cleaning gas injection ports

ABSTRACT

A method and arrangement for the insitu cleaning of a chamber in which process gas is injected into the chamber through gas injection ports. Separate gas injection ports through which process gas and the cleaning gas are injected into the chamber are provided. The process gas is injected into the chamber, such as a plasma chamber, through a first gas injection port while the cleaning gas, which cleans the residue left by the process gas during the deposition process, is injected into the chamber through the second gas injection port that is separate from the first gas injection port through which the process gas is injected. The separation of the gas injection ports provides an equalized pressure within the jet screw ports for the process gas and the interior of the chamber. This allows the jet screw ports to be maximally cleaned and reduces the frequency of replacement of the jet screw ports in the chamber.

FIELD OF THE INVENTION

The present invention relates to the field of chemical vapor depositionsystems, and more particularly, to apparatus and methods for cleaningthe residue left by the process gas which has been injected into aplasma chamber of the system.

BACKGROUND OF THE INVENTION

Chemical vapor deposition (CVD) systems normally employ a chamber inwhich gaseous chemicals react. From these reactions, a substance isdeposited on a wafer surface to form dielectric, conductor, andsemiconductor film layers that constitute an integrated circuit, forexample. In a chemical vapor deposition system, a process gas isinjected into the plasma chamber in which a plasma is formed. Due to theion bombardment within the plasma of the process gas, (SiH₄(silane), forexample) silicon will be deposited on a wafer which has been previouslyplaced in the chamber. During this deposition step, the gas injectionports, also known as jet screws, typically clog with silicon-rich oxideresidue formed by the combined SiH₄ (the process gas) and oxygenradicals flowing to the gas injection port. These oxygen radicalsoriginate from the plasma chamber.

The residue coats the walls of the chamber, and also tends to clog thegas injection ports. The chamber, as well as the gas injection ports,needs to be cleaned periodically. This ensures that each waferencounters the same environment so that the deposition process isrepeatable. Since opening up the chamber (changing out the hardware) forcleaning is very labor intensive and costly, a method for removing thedeposition from the chamber walls without opening the chamber itself hasbeen previously developed. This “insitu” cleaning has been accomplishedin the past using fluorine. The fluorine is injected into the chamber asNF₃. Fluorine is known to etch silicon and silicon dioxide at high rateswhen it is accompanied by ion bombardment. Radio frequency (RF) powerprovides the energy for ion bombardment, with the NF₃ serving as thesource of fluorine.

Typically, after a wafer is processed through deposition in the CVDsystem, the wafer is removed to a load lock. A cover wafer is thentransferred to the chamber and placed on the chuck. The cover wafer is astandard silicon wafer that is coated with aluminum. It protects thechuck surface from the plasma cleaning and conditioning steps thatfollow.

The RF power is applied to the chamber and NF₃ is injected into thechamber. The walls will then be cleaned of oxide deposition. However,there may still be a significant amount of fluorine in the chamber andon the walls and free particles. For this reason, a pre-depositionconditioning step is often required. The conditioning step isessentially a deposition that getters the fluorine and tacks downparticles onto the chamber walls. When this pre-deposition conditioningstep is completed, the cover wafer is transported back to its cassetteand the next wafer can then be processed.

In conventional systems for routing the gas to the chamber, injectionports are shared between the deposition process gas (SiH₄) and theinsitu cleaning gas (NF3). Such an arrangement is shown in prior artFIG. 1 in which a portion of a process chamber is schematicallydepicted. The plasma chamber 10 injects oxygen at port 12 into theinterior 14 of the plasma chamber. The oxygen radicals are formed withinthe plasma chamber 14. The shared injection ports for the depositionprocess gas and the insitu clean gas are depicted as reference numeral16. During the deposition step, the gas injection ports (also known as“jet screws”) clog with silicon-rich oxide residue formed by thecombined SiH₄ and the incoming oxygen radicals originating from theplasma chamber.

As stated earlier, the insitu cleaning gas is designed to chemicallyetch the SiO₂ (silicon dioxide) residue. However, high pressure causedby supersonic gas flows in front of the jet screws causes regions ofscarce fluorine radicals that reduce fluorine induced etching of theSiO₂. FIG. 2 a schematic depiction of a detail of a jet screw. NF₃ gasis injected into the chamber 14 through the jet screw 16. Within the jetscrew, there is SiO₂ clogging, schematically depicted at point 18 at thejet screw 16. The high pressure region 20 of scarce fluorine radicalscaused by the supersonic gas flows in front of the jet screws 16 reducesthe fluorine induced etching of the SiO₂ in this area, and inparticular, prevents the jet screws 16 from being unclogged of the SiO₂residue. All of the other chamber surfaces are typically cleaned exceptfor the jet screw ports.

Due to the SiO₂ clogging of the jet screw ports, the jet screws arenormally replaced after approximately 300 wafers have been processed.This process involves shutting down the chamber at high expense and lossof productivity. Another problem of the prior art arrangement is thatthe SiH₄ and NF₃ gases, if combined, are highly combustible so thatrouting the gases through the same injection ports can be relativelydangerous.

SUMMARY OF THE INVENTION

There is a need for a gas routing system and method for routing gas in aplasma chamber so as to unclog the jet screws through which depositiongas is injected into the chamber.

These and other needs are met by the present invention which provides anarrangement for insitu cleaning of a chamber in which process gas isinjected into the chamber through gas injection ports. The arrangementcomprises a chamber in which a process is performed, and at least afirst gas injection port in the chamber through which the process gas isinjectable into the chamber. At least a second gas injection port isprovided in the chamber through which insitu cleaning gas is injectableinto the chamber. The cleaning gas injected into the chamber alsocontacts the first gas injection port to clean the first gas injectionport. The first and second gas injection ports are separate ports.

By re-routing of the cleaning gas through a separate, second gasinjection port, the pressures within the jet screws are equalized withthe pressure of the chamber. This allows higher fluorine dissociationand SiO₂ etching.

Another advantage of the present invention is the injection of the SiH₄and NF3 gases through completely separate manifolds, thus providing aclear safety advantage.

A further advantage of the present invention is the reduction in theamount of maintenance required of the chamber. For example, using thegas routing system of the present invention, the chamber does not needto be maintained for approximately 3,000 wafers. This is a decidedadvantage over the prior art in which the jet screws needed to bereplaced after only 300 wafers.

Another advantage of the present invention is that the insitu clean timeis decreased due to more efficient cleaning of the jet screws. Thisprovides a throughput advantage of, for example, two wafers per hour.Finally, another advantage is that plasma to surface arcing iscompletely eliminated in the jet screw area.

Another embodiment of the present invention satisfies the earlier statedneeds by providing a method of routing gas to a plasma chambercomprising the steps of: injecting process gas into the plasma chamberthrough a first gas injection port, and injecting chamber gas into theplasma chamber through a second gas injection port. The second gasinjection port is separate from the first gas injection port. Thecleaning gas cleans the plasma chamber and the first gas injection port.

Another method of the present invention provides for unclogging jetscrew ports in the chamber. The jet screw ports inject process gas intothe chamber. This method comprises the steps of terminating injection ofthe process gas into the chamber and injecting cleaning gas into thechamber through openings separate from the jet screw ports to equalizepressure of the cleaning gas within the jet screw ports with pressure ofthe cleaning gas within the chamber.

In another embodiment of the present invention, an electron cyclotronresonance chemical vapor deposition system is provided. This systemincludes an electron cyclotron resonance plasma chamber, and a gassupply that supplies plasma forming gas, process gas, and cleaning gasto the plasma chamber. The plasma chamber has a first port through whichthe process gas is supplied, and a second port, separate from the firstport, through which the cleaning gas is supplied.

The foregoing and other features, aspects and advantages of the presentinvention will become more apparent from the following detaileddescription of the present invention when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1, as described supra, is a schematic depiction of a portion of aprocess chamber in accordance with the prior art.

FIG. 2, as described supra, is a schematic depiction of a detail of aportion of the process chamber.

FIG. 3 is a schematic cross-sectional diagram of an electron cyclotronresonance chemical vapor deposition system constructed in accordancewith an embodiment of the present invention.

FIG. 4 is a schematic cross-sectional diagram of a chemical vapordeposition system constructed in accordance with another embodiment ofthe present invention.

DETAILED DESCRIPTION OF THE DRAWINGS

A schematic depiction of a cross-section of an electron cyclotronresonance (ECR) chemical vapor deposition (CVD) system constructed inaccordance with an embodiment of the present invention is provided inFIG. 3. The system includes an electron cyclotron resonance plasmachamber 30 having a 2.45 GHz microwave power supply 32. The microwavespass through a microwave window 34 into the plasma chamber 30. A quartzliner 36 lines the interior of the plasma chamber 30.

Plasmas are generated by the ionization of gas molecules. This may beaccomplished by an energetic electron striking a neutral molecule.Electrons can also cause dissociation and other excitations. Theelectrons are excited by electric fields such as RF and microwaves. Assuch, these are the conventional methods for generating processingplasmas.

In contrast to conventional plasmas that typically operate at pressuresgreater than 70 millitorr, high density plasmas generally operate atpressures in the range of 0.5 to 10 millitorr. The ion to neutral ratiocan be as high as one in a hundred (compared to less than one in amillion in low density plasmas). Ion densities can be more than 1E12 percubic centimeter. Such plasmas require sophisticated plasma generationtechniques such as electron cyclotron resonance.

In an electron cyclotron resonance plasma chamber, the electron angularfrequency due to the magnetic field matches a microwave frequency, sothat electron cyclotron resonance occurs. In this state, electrons gainenergy from the microwave source and accelerate in a circular motion.The cross-section for ionization is therefore effectively increased,allowing for the creation of high density plasma at low pressure.

The magnetic field is also used to extract the ions out of the plasmasource. The ions follow the lines of induction toward the wafer. Theplasma tends to be cone-shaped due to the divergent magnetic field. Thedivergent magnetic field creates a force that pulls the electrons out ofthe plasma chamber. The resulting potential extracts ions to form avaried directional plasma stream.

The divergent magnetic field is created by a primary coil 38 thatsupplies the 875 Gauss that is needed for the electron cyclotronresonance condition. This primary coil 38 also provides the divergentmagnetic field for ion extraction.

Auxiliary magnetic coils 40 are provided behind a wafer holder assembly42 to shape the plasma into the desired shape. The wafer holder assembly42 holds a wafer (not illustrated in FIG. 3). The wafer holder 42includes a 13.56 MHz RF power supply (up to 2500 W). The RF power supplyprovides, along with the microwaves, the electric fields that excite theelectrons to generate the processing plasma.

An electrostatic chuck is provided to hold the wafers within a reactorchamber 48. The use of an electrostatic chuck obviates the need formechanical clamping of the wafer. Wafer cooling is provided by helium,for example, to the underneath or backside of the wafer through a heliumsupply line 50. Closed-loop control of the helium pressure regulates thewafer temperature during deposition. Insitu wafer temperature monitoringis provided through a temperature probe 52 which sends its sensorsignals to a controller (not depicted). A 3,000 1/sec turbomolecularpump with a base pressure less than 1×10⁻⁶ Torr is used to control thepressure within the plasma chamber 30 and the reactor chamber 48.

A wafer transport mechanism (not depicted) is provided for transportingwafers into and out of the reactor chamber 48. A conventional wafertransport system may be used for this purpose.

In certain embodiments of the present invention, oxygen and argon areprovided into the plasma chamber 30 from a gas supply through aninjection port 60. Plasma will be generated in the plasma chamber uponapplication of the RF energy and microwave energy by the RF generator 44and the microwave generator 32.

Once a wafer base has been transported into the reactor chamber 48 bythe wafer transport system and placed onto the electrostatic chuck 46,and a plasma has been generated within the plasma chamber 30, thedeposition gas (SiH₄, for example,) is introduced into the plasmachamber 30 through one or more gas injection ports 62 that are separatefrom the gas injection port through which the gas to form the plasma isprovided. The gas injection ports 62 are jet screws, for example. Duringdeposition, these jet screws, along with the remaining surfaces of theplasma chamber 30 and the reactor chamber 48, become coated with aresidue (SiO₂). This residue should be cleaned from the surfaces of thechamber and the interior of the jet screws 62 between the processing ofeach wafer, so that each wafer will encounter the same environment,thereby making the process repeatable. Accordingly, the cleaning gas(NF₃, in the exemplary embodiment of the present invention) isintroduced into the plasma chamber and RF power is applied from the RFgenerator 44 to the plasma chamber 30.

As discussed earlier, in the prior art arrangement, the jet screw ports62 become clogged with the SiO₂ residue, and injection of the NF₃cleaning gas through the jet ports 62 produced a high pressure region inthe plasma chamber 30 directly in front of the jet screw during theinsitu cleaning step. This caused a poor fluorine dissociation due tothe high localized pressure in front of the jet screw ports 62. As aconsequence, there was not a sufficient amount of fluorine radicals toreact with the SiO₂ to clean the jet screw ports 62 sufficiently. Sincethe jet screw ports 62 were not being cleaned sufficiently during insitucleaning, their frequent replacement, for example after approximately300 wafers, was required.

In the present invention, as depicted in FIG. 3, the NF₃ cleaning gas isinjected into the plasma chamber 30 through injection port 60, the sameport through which the oxygen and argon gas is injected. This injectionport 60 is separate from the injection ports (jet screw ports) 62through which the deposition gas is injected. In other embodiments ofthe invention, the cleaning gas is injected in a dedicated port,exclusively devoted to cleaning gas injection. Such an embodiment isdepicted in FIG. 4, in which the cleaning gas is injected through itsown dedicated port 63, the oxygen and argon gas being injected throughinjection port 60, and the SiO₂ being injected through the jet screwports 62.

The routing of the cleaning gas to be injected into the plasma chamber30 through a port separate from the injection port through which thedeposition gas is injected has a number of advantages, including theequalization of pressure within the jet screw 62 and the plasma chamber30 during insitu cleaning. This prevents the high pressure region in theplasma chamber 30 and jet screw 62 from forming. As a consequence, thereis no longer a poor fluorine disassociation due to the high localizedpressure in front of the jet screws 62. The jet screws 62 will thereforebe cleaned to relatively the same extent as the other surfaces of theplasma chamber 30.

Another advantage provided by the separate routing of the cleaning gasand the deposition gas is related to safety. As stated earlier, the SiH₄and NF₃ gases are highly combustible if combined. Their separationaccording to the present invention provides a clear safety advantage.Also, all plasma to surface arcing is eliminated in the area of the jetscrew ports 62. Further, the superior cleaning performance within thejet screw 62 eliminates the need for replacing the jet screws after only300 wafers. The inventors have found that no maintenance is required inthe plasma chamber 30 for approximately 3,000 wafers. This is anextremely significant advantage in reducing the amount of downtime formaintenance of the chamber. Related to this, the insitu clean time isalso decreased due to a more efficient cleaning of the jet screw ports62. For example, a throughput advantage of approximately at least 2wafers per hour may be realized using the gas routing system of thepresent invention. Where the processing of a single wafer provides highprofits, the throughput of the wafers is critical.

An exemplary embodiment of the operation of the invention is as follows.After the deposition process has been completed, and the deposition gasis no longer being supplied to the plasma chamber 30, the wafer beingprocessed is removed by the wafer transport system to the load lock. Atthis point, a cover wafer is transferred to the reactor chamber 48 andplaced on the electrostatic chuck 46. The cover wafer is a standardsilicon wafer that is coated with aluminum. The purpose of the coverwafer is to protect the chuck surface from the plasma cleaning andconditioning step.

Once the cover wafer is in place, the RF power is applied to the plasmachamber 30 and the NF₃ cleaning gas is injected in the plasma chamber 30through port 60. After the walls of the chamber 30 and the jet screwport 62 have been cleaned of oxide deposition, there is still a fairamount of fluorine in the chamber 30 and on the walls, as well as freeparticles. For this reason, a pre-deposition conditioning step may beused. The conditioning step is essentially a deposition that getters thefluorine and tacks down particles. When this pre-deposition conditioningstep is completed, the cover wafer is then transported back to itscassette and the next wafer can then be processed.

Although the present invention has been described with an electroncyclotron resonance chemical vapor deposition system, the invention alsofinds use in other types of systems employing a plasma chamber in whicha deposition gas is injected, leaving a residue that must be cleaned byan insitu cleaning gas. Also, although an exemplary embodiment has beendescribed with specific gases for the deposition gas, the oxygen andargon forming gases, and the cleaning gas, the invention is not limitedto such gases, and may be used with other types of gases withoutdeparting from the spirit or scope of the present invention.

Although the present invention has been described and illustrated indetail, it is to be clearly understood that the same is by way ofillustration and example only and is not to be taken by way oflimitation, the spirit and scope of the present invention being limitedonly by the terms of the appended claims.

What is claimed is:
 1. A method of unclogging a first port in a vacuum chamber for processing workpieces, the first port injecting gas into the chamber, the method comprising the steps of: terminating injection of the process gas into the chamber, then, while injection of the process gas into the chamber is terminated and the chamber remains in vacuo and the port is clogged, applying r.f. plasma excitation power to a structure including the first port while injecting cleaning gas into the chamber through a second opening separate from the first port to equalize pressure of the cleaning gas within the first port with pressure of the cleaning gas within the chamber. , the cleaning gas being converted to a plasma by r.f. plasma excitation power applied to it via the structure.
 2. The method of claim 1, further comprising supplying energy into the chamber in the presence of the cleaning gas to generate ion bombardment, with the cleaning gas providing a cleaning agent that etches depositions in the chamber and the first port when the ion bombardment is generated.
 3. The method of claim 2 1, wherein the chamber has a chuck onto which wafers are placed, the method further comprising placing a cover wafer on the chuck prior to injecting the cleaning gas.
 4. The method of claim 3, further comprising performing a deposition after the cleaning agent etches the deposits to getter the cleaning agent, followed by removing the cover wafer from the chamber.
 5. The method of claim 1 wherein the first port comprises a jet screw port.
 6. A method of processing workpieces in a vacuum plasma processing chamber and cleaning the chamber while the workpieces are not being processed comprising processing the workpieces in the chamber while the chamber is in vacuo by introducing a processing gas into the chamber through a first port and applying electric energy to the processing gas to establish a plasma that processes the workpiece, the processing gas having a tendency to form a residue that clogs the first port, the first port while clogged and while gas is applied to it establishing a high pressure region which resists the flow of gas through the first port into the chamber, and while the workpieces are not being processed and the chamber remains in vacuo, applying, r.f. plasma excitation power to a structure including the first port while applying a cleaning gas to the chamber through a second port separate from the first port in such a manner that pressure is equalized at the first port and the cleaning gas unclogs the first port of the residue and cleans the remainder of the chamber.
 7. The method of claim 6 further comprising introducing a second processing gas into the chamber through the second port during vacuum plasma processing of the workpieces, the second processing gas being of a type that (a) does not have a tendency to form a residue in the second port and (b) reacts chemically with the first reaction gas.
 8. The method of claim 7 wherein the second processing gas includes argon and oxygen.
 9. The method of claim 8 wherein the first processing gas includes SiH₄ and the residue comprises SiO₂.
 10. The method of claim 6 wherein gas is not introduced into the chamber through the second port during workpiece processing and further comprising introducing another reaction gas into the chamber via a third port during workpiece processing, the reaction gases introduced into the chamber via the first and third ports chemically reacting during workpiece processing.
 11. The method of claim 6 wherein no gas flows through the first port while the cleaning gas is applied to the chamber through the second port.
 12. The method of claim 6 wherein the first port comprises a jack screw.
 13. The method of claim 6 wherein the chamber includes a workpiece holder, and covering the workpiece holder while the cleaning gas is applied to the chamber via the cleaning port.
 14. The method of claim 6 wherein the cleaning gas is NF₃.
 15. The method of claim 6 further including applying electric energy to the cleaning gas to establish a plasma that cleans the first port of the residue and the chamber.
 16. The method of claim 6 further comprising applying a getter to the chamber after the cleaning gas has been applied and before workpiece processing begins, the getter removing residual atoms of the cleaning gas from the chamber.
 17. A method of cleaning a vacuum processing chamber between workpiece processing operations wherein the workpiece processing is performed by supplying processing gas to the chamber via a first port while the chamber is in vacuo, the processing gas having a tendency to leave a clogging residue in the first port, the chamber including a second port separate from the first port, the method comprising applying r.f. plasma excitation power to a structure including the first port while introducing a cleaning gas into the chamber via the second port while the chamber remains in vacuo and the processing gas is not supplied to the chamber so pressure is equalized at the first port and the cleaning gas cleans the first port of the clogging residue as well as the remainder of the chamber. , the cleaning gas being converted to a plasma by r.f. plasma excitation power applied to it via the structure.
 18. The method of claim 17 wherein the cleaning gas is NF₃.
 19. The method of claim 18 further including applying electric energy to the cleaning gas to establish a plasma that cleans the first port of the residue and the chamber.
 20. The method of claim 17 further including applying electric energy to the cleaning gas to establish a plasma that cleans the first port of the residue and the chamber. 